In recent years materials, in particular for organic light-emitting diodes, have become known, which improve the electron injection and the electron transport in OLED's. (Pat.: Novaled GmbH Dresden DE-10307125_A1 Jan. 8, 2004)
This also results in a lower operating voltage without affecting the efficiency of the OLED.
These materials are available as precursors and are converted into strong electron donors by the vapor depositing process, where, co-vaporized with the electron transporter, they are doped in small quantities into the electron-transporting layer or the emitter layer of the OLED (n-doping). This leads to an electronic interaction with the electron-transporting material or the emitter, which is the reason why such additions facilitate the reduction of the electron transporting material or the emitter material (i.e. acceptance of electrons into the LUMO [lowest unoccupied molecular orbital] of the electron-transporting or emitter material), which otherwise takes place due to the energy of the electric field only. Therefore, a weaker electric field (i.e. a lower operating voltage) achieves the same efficiency which without these materials could be provided only by a stronger electric field.
However, in the currently known materials, especially the stability and the injection and electron transport-facilitating effect is not satisfactory yet.